The present invention relates to a method of manufacturing a ferroelectric thin film and a method of manufacturing a ferroelectric memory, particularly to improve the crystallinity of the ferroelectric thin film.
The ferroelectric memory being researched now is divided into two main areas. One is directed to a system for detecting reverse charge quantity of a ferroelectric capacitor constructed with the ferroelectric capacitor and a selective transistor.
Another is directed to a memory of a system for detecting a change of resistance of a semiconductor caused by a spontaneous polarization of the ferroelectric substance. A typical example of this type of system is a MFSFET. This is an MIS structure using the ferroelectric substance for a gate insulating film.
In any structure, it is known that film quality of the ferroelectric substance affects the characteristics of memory significantly.
Then, various methods for improving the crystallinity of the ferroelectric thin film are proposed. As one of them, a method of crystallization of a PZT thin film called Ti seed method is proposed.
As shown in FIG. 7, the method includes forming a seed layer 9L consisting of titanium ultra thin film of about 20 nm film thickness on a surface of a lower electrode 8 consisting of platinum Pt and the like by spattering method and to form a PZT film 9P on the upper layer by sol-gel method as shown in FIG. 7. Here, mixed solution of Pb(CH3COO)2.3H2O, Zr(t-OC4H9)4, and Ti(i-OC3H7)4 is used as a starting material, after spin-coating the mixed solution, is dried at 150° C., and temporary baking of 400° C. for 30 minutes is performed under a dry air atmosphere. After repeating this five times, crystal growth from the ultra thin film 9L appears through crystallization annealing process of about 700° C., one minute in atmosphere of O2.
In the method, there has been a problem that particle diameter of crystal can not be controlled because a place where crystallization starts is unstable and dispersion of characteristic is large because uniform size columnar crystal is formed so as not to obtain suitable characteristics, particularly at micronization and high integration.
There has been a problem that the method has a place becoming titanium oxide layer (TiO2) or lead titanate (PbTiO3) layer without becoming PZT film so as to obtain good characteristics.
There has been a problem that the method negatively affects the substrate layer, for example, by negatively affecting substrate wiring because the temperature at crystallization annealing is high at about 700° C.